http://support.intel.com/support/processors/mobile/pm/sb/CS-007967.htm
From that chart - you'll see the P4-M's have a 1mb cache (well, this one would) whilst this same Centrino has the 2mb cache. The other features such as dedicated stack manager, EIS technology make the CPU outperform the P4-M quite easily.
Results page of an interesting review:
http://www.anandtech.com/mobile/showdoc.aspx?i=1800&p=15
I don't have the time to find the time to find it right now but somewhere on the Intel site is their cross comparison chart of the Pentium M vs P4 line with comparisons of the speed. Basically it states a 1.7ghz Centrino/Pentium M is the equiv. of a P4 2.6ghz.